Process for producing propylene oxide

Details Process for producing propylene oxide Process for producing propylene oxide

2002-01-11

2003-11-11

Trinh, Ba K. (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S541000

Reexamination Certificate

active

06646138

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a process for producing propylene oxide. More particularly, the present invention relates to a process for producing propylene oxide in which propylene is converted into propylene oxide in high yield using a hydroperoxide of isopropylbenzene as an oxygen carrier and said isopropylbenzene can be recycled.
2. Background Art
A process for oxidizing propylene by using a hydroperoxide of ethylbenzene as an oxygen carrier to obtain propylene oxide and styrene is known as a Halcon process. This process, however, is unsatisfactory from the standpoint of selective production of only propylene oxide in high yield, since styrene is by-produced together with propylene oxide.
SUMMARY OF THE INVENTION
The present inventors have intensively studied a process for producing propylene oxide not having the above-mentioned problem, resultantly found that propylene can be converted into propylene oxide without production of by-products by using a hydroperoxide of isopropylbenzene as an oxygen carrier and propylene oxide can be obtained at high yield by adding a process for removing an organic acid, and thus completed the present invention.
Namely, the present invention relates to a process for producing propylene oxide comprising the following steps:
oxidation step: a step of obtaining isopropylbenzene hydroperoxide by oxidizing isopropylbenzene;
epoxidation step: a step of obtaining propylene oxide and cumyl alcohol by reacting propylene with isopropylbenzene hydroperoxide obtained in the oxidation step;
hydrogenolysis step: a step of obtaining isopropylbenzene by hydrogenolyzing cumyl alcohol obtained in the epoxidation step, and recycling this isopropylbenzene to the oxidation step as a raw material of the oxidation step; and
organic acid removal step: a step of removing an organic acid out of the system in at least one point in said steps or between said steps.
DETAILED DESCRIPTION OF THE INVENTION
The oxidation step in the present invention is a step for obtaining isopropylbenzene hydroperoxide by oxidizing isopropylbenzene. The oxidation of isopropylbenzene is usually conducted by auto-oxidation using an oxygen-containing gas such as air, oxygen-concentrated air or the like. Particularly, an emulsion oxidation method in an alkaline aqueous emulsion is preferable from the standpoint of improving the yield of isopropylbenzene hydroperoxide. The usual reaction temperature is from 50 to 200° C., and the reaction pressure is usually from atmospheric pressure to 5 MPa. In the emulsion oxidation method, an alkali metal compound such as NaOH or KOH, alkaline earth metal compound, or alkali metal carbonate such as Na
2
CO
3
or NaHCO
3
, NH
3
, (NH
4
)
2
CO
3
, alkali metal ammonium carbonates or the like is used as an alkaline reagent.
The epoxidation step in the present invention is a step of reacting an organic hydroperoxide obtained in the oxidation step with propylene to obtain propylene oxide and cumyl alcohol. The epoxidation step is preferably carried out in the presence of a catalyst comprising a titanium-containing silicon oxide from the viewpoint of obtaining the object matter under high yield and high selectivity. As these catalysts, so-called Ti-silica catalysts containing Ti chemically bonded to silicon oxide are preferable. For example, a compound prepared by supporting a Ti compound on a silica carrier, a compound prepared by combining a Ti compound with silicon oxide by a coprecipitation method or sol gel method, zeolite compounds containing Ti, and the like are listed.
It is preferable that such a titanium-containing silicon oxide satisfies all of the following conditions (1) to (3).
The condition (1) is that an average pore diameter is 10 Å or more.
The condition (2) is that pores in 90% or more of volume of all pores, have a pore diameter of from 5 to 200 Å.
The condition (3) is that a specific pore volume is 0.2 cm
3
/g or more.
Here, the above-mentioned specific pore volume means a pore volume per g of a catalyst.
The measurements in the above-mentioned conditions (1) to (3) can be conducted by ordinary methods using a physical adsorption method for a gas such as nitrogen, argon or the like.
It is preferable that the titanium-containing silicon oxide satisfies the following condition (4) in addition to the above-mentioned conditions (1) to (3).
The condition (4) is that a titanium-containing silicon oxide is obtained by using a quaternary ammonium ion of the following general formula (I) as a template and then removing the template.
[NR
1
R
2
R
3
R
4
]
+
  (1)
(wherein, R
1
represents a linear or branched hydrocarbon group having 2 to 36 carbon atoms, and R
2
to R
4
represent an alkyl group having 1 to 6 carbon atoms.).
R
1
is a linear or branched hydrocarbon group having 2 to 36 carbon atoms, preferably having 10 to 18 carbon atoms. R
2
to R
4
are an alkyl group having 1 to 6 carbon atoms, and it is preferable that all of R
2
to R
4
are a methyl group. As the specific examples of the quaternary ammonium ion of the general formula (I), cations such as hexadecyltrimethylammonium, dodecyltrimethylammonium, benzyltrimethylammonium, dimethyldidodecylammonium, hexadecylpyridinium and the like can be listed.
As the method for removing a template, removal by a calcination, removal by an extraction, and the like are listed, and the extraction is preferable for maintaining activity and selectivity of a catalyst at high level. It is preferable that the catalyst has an absorption peak in the region of 960±5 cm
−1
in the infrared absorption spectrum. This peak is supposed to correspond to titanium introduced in a silica skeleton. A catalyst can be used in any physical forms such as a powder, flake, spherical particle and pellet. As the specific and preferable methods for obtaining a catalyst, the following methods can be listed.
First, a silica source, a titanium source and a quaternary ammonium ion as a template are mixed and stirred in liquid condition to obtain a solid containing the catalyst components and template. When a reagent used is in the form of solid, it is advantageous to dissolve or disperse the reagent in a solvent to give a solution to be used.
As the silica source, amorphous silica and alkoxysilanes, for example, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate and the like are listed.
As the titanium source, titanium alkoxides, for example, tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraisobutyl titanate, tetra-2-ethylhexyl titanate, tetraoctadecyl titanate, and titanium (IV) oxyacetylacetonate, titanium (IV) diisopropoxy bisacetylacetonate and the like, or halogenated titaniums, for example, titanium tetrachloride, titanium tetrabromide, titanium tetraiodide and the like, are listed.
As the template, those described above can be used.
As the examples of the solvent, water and alcohols, for example, methanol, ethanol, n-propanol, 2-propanol, n-butanol, sec-butanol, t-butanol, vinyl alcohol, allyl alcohol, cyclohexanol, benzyl alcohol and the like, diols, or mixtures thereof, and the like are listed.
The molar ratio of the use amount of a titanium source to the use amount of a silica source is preferably from 10
−5
to 1, more preferably from 0.00008 to 0.4. The molar ratio of the use amount of a quaternary ammonium ion to the total amount of a silica source and a titanium source is preferably from 10
−2
to 2.
For promoting the reaction of a silica source and a titanium source, it is preferable to impart alkaline or acidic property to a mixed solution. As the alkali source, quaternary ammonium hydroxides are preferable, and examples thereof include tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide and the like. As examples of the acid, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and the like, and organic acids such as formic acid, acetic acid, propionic aci

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